Complete issue - IMA Fungus

old, and are interpreted as representing
stratified thalli, one with a cyanobacterial
partner (Cyanolichenomycites devonicus)
and one with a green algal partner
(Chlorolichenomycites salopensis). The
structures were compared with modern
freshly collected lichens which had been
“charcoalified” to facilitate comparison
with the Lowe Devonian specimens. The
results are remarkable and leave no doubt
that complex stratified lichen thalli similar
to that seen in extant Lecanoromycetes had
already evolved by this early date. These
predate the earliest previous reports of
fossil stratified lichens from the Triassic
by some 195 Myr. The paper is also of
value in including a critical assessment of
previously discovered fossils that have been
interpreted as lichens, including citations of
several papers scarcely known outside the
palaeobotanical community.
Of further interest is that
while no ascomata were found, the
Cyanolichenomycites had what is clearly a
pycnidium, within which young conidia and
conidiophores were visualized by superbly
skilled scanning electron microscopy.
This is an extraordinarily meticulously
executed and elegant study, and I
understand that there will be future papers
documenting other fascinating fungal
fossils from these ancient deposits. Such
fossils have major implications for the
calibration of molecular clocks and the
dating of divergence points in phylogenetic
trees. In this case the authors are confident
their two fossils belong to Pezizomycotina,
but, perhaps over-cautiously, prefer not
to refer them to a class in the absence of
any sexual reproductive structures despite
the obvious structural similarity to extant
Lecanoromycetes. However, I do feel that
possible classification now needs to be
considered in future attempts to reconstruct
and date the origins of that class, and of
lichenization itself, even in the absence of
ascomata. Structurally differentiated lichen
thalli had clearly started to develop well
before the Lower Devonian to enable such
complex fossil to have been around by that
time.
Honegger R, Edwards D, Axe L (2013) The earliest
records of internally strafified cyanobacterial
and algal lichens from the Lower Devonian of
the Welsh borderland. New Phytologist 197:
264–275; DOI 10:1111/nph.12009.
RESEARCH NEWS
Trichoderma trichothecenes in biocontrol and
plant defence gene induction
Molecular tools are increasingly enabling us
to understand something of the complexity
of interactions between different fungi
and plants. Some Trichoderma species
produce trichothecenes, most importantly
trichodermin and harzianum A (HA),
but the genes encoding these have a
different genomic organization from
that seen in trichothecene producing
gene clusters of Fusarium species. There
have been some previous studies on the
effects of trichodermin produced by T.
brevicompactum on plants, but the role
of harzianum A had remained obscure.
Now, the pertinent genes in a transformed
strain of T. arundinaceum, labelled tri4
and involved in HA biosynthesis, were
silenced, enabling Malmierca et al. (2012)
to explore its effects and possible relevance
to the use of the fungus in biocontrol. They
demonstrated that disruption of this gene
led to reduced antifungal activity against
both Botrytis cinerea and Rhizoctonia solani,
and further to a reduced ability to induce
the expression of plant defence related genes
in tomato plants compared to the wildtype
Trichoderma strain. Their experiments
lead to the conclusion that harzianum A
has a role in sensitizing the tomato plants
to attack by other fungi, as well as in its
antifungal mycoparasitic activity. They also
found that the plant pathogenic fungi and
the tomato plants had a role in regulating
the expression of the tri genes in T.
arundinaceum.
Schematic representation of the network of interactions established among Trichoderma arundinaceum
(Ta37), Botrytis cinerea, and tomato plants deduced from the present work. Arrows indicate response
stimulation or gene upregulation, and blunt-ended lines indicate gene repression or growth inhibition.
Red, blue, and green lines indicate interactions mediated by B. cinerea, tomato plant, and the Trichoderma,
respectively. a, sensitizing effect of Trichoderma-pretreated tomato plants mediated by the trichothecene
harzianum A (HA); b, coupled action of HA and extracellular hydrolytic enzymes to inhibit B. cinerea growth;
c, other metabolites produced by T. arundinaceum that, in addition to HA, would also affect its interaction
with plants and with its fungal targets. Reproduced from Malmierca et al. (2012).
volume 3 · no. 2
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